The invention relates to a device for tensioning the chains of crawler-type or tracked vehicles, in particular the chains of hydraulic excavators.
The document DE-C 35 07 805 discloses a device for tensioning the chains of tracked vehicles, with a first hydraulic cylinder for tensioning the chain deflection wheel, which is positioned in a bearing that is positioned displaceable in the center plane for the chain, wherein this first hydraulic cylinder is connected to a second hydraulic cylinder such that a floating piston, is arranged together with a return valve, which connects the chamber halves separated by the piston, and blocks the return flow from the first hydraulic cylinder. The piston can be displaced inside an additional hydraulic cylinder, between front and back end stops, wherein the displacement distance corresponds to a volume of the hydraulic fluid, which is required for relaxing the load on the previously tensioned chain, so as to achieve the most favorable chain tension. In the region of the back end stops, the second hydraulic cylinder is connected to a feed line for feeding in pressure medium and, in the region of the front end stops, with a return-flow line for discharging the pressure medium with a pressure corresponding to the chain tensioning pressure. The feed line is connected to the tank once the piston has been moved against the front end stop.
With this prior art, the hydraulic cylinders are arranged in a line, meaning one behind the other, which results in a relatively long structural length. As a result, the cylinders are positioned extremely close to the guide wheel, are subject to contamination, and can be maintained only with great difficulty.
The document DE 31 04 323 A1 discloses a tensioning device that acts upon the circulating chain of a tracked vehicle and preferably upon a guide wheel of a chain-type tracked vehicle. The tensioning device is embodied as working cylinder connected to a pressure-controlled hydraulic source, the cylinder chamber of which guides a tensioning piston pushing against the guide wheel, which is provided with a pressure-relief valve and has a return valve installed in the intake for the hydraulic medium source. The tensioning piston is guided inside a holding cylinder, which in turn is embodied as holding piston guided inside the working cylinder. The piston bottom of the holding piston is provided with an opening into which a second return valve is inserted. The disadvantage of said double cylinder is that if the return valve in the piston bottom of the holding piston fails, the double cylinder must be taken apart completely.
The DE 18 10 354 discloses a device for tensioning and supporting the drive chains on a tracked vehicle, comprising an adjustable support and a support for the guide wheels that is dependent on the chain tensioning force. The adjustable support consists of a piston-cylinder unit for a pressure medium with high viscosity (grease). The tension-force dependent support is composed of a piston-cylinder unit for a pressure medium with low viscosity (oil), wherein the pressure medium can be diverted from the pressure-medium drive of the chassis. The piston-cylinder units are arranged coaxial and combined into one structural unit.
As a result of the incompressibility of the different media that are used (grease—oil), it is possible that the hydraulic circulation builds up, in particular when traveling over uneven terrain, so that damages can possibly occur.